Configurations in Entity Framework Core

Last Updated: September 24, 2022

Entity Framework Core Configurations allow us to override the default conventions in order to create database schema and mappings in the way we want. We already saw the concept of Conventions in Entity Framework Core where we understood how default conventions work. If we want to override the conventions then apply the configurations and customize the EF Core model to database mappings.

Page Contents

This tutorial is a part of Entity Framework Core series.

There are 2 Entity Framework Core Configuration Methods:

1. Data Annotation Attributes
2. Fluent API

Let us understand them one by one.

Data Annotation Attributes

These are the .NET Attributes that can be applied to the domain classes and their properties. The Data Annotation attributes are included in separate namespace called System.ComponentModel.DataAnnotations.

Let me demonstrate how to apply these Data Annotation Attributes to the domain classes in order to configure database tables and override the default Conventions of Entity Framework Core.

In the below code we have applied Data Annotation Attributes to the 2 domain classes (Country & City) and their properties.

[Table("TBL_City")]
public class City
{
    [Key]
    public int KeyId { get; set; }
 
    [Column("CityName", TypeName = "varchar(25)")]
    public string Name { get; set; }
 
    [NotMapped]
    public int Population { get; set; }
 
    [ForeignKey("FKid")]
    public Country Country { get; set; } 
}

[Table("TBL_Country")]
public class Country
{
    [Key]
    public int KeyId { get; set; }
 
    [MaxLength(20)]
    public string Name { get; set; }
}

Once we apply Entity Framework Core Migration then 2 database tables will be created due to [Table("Name")] attribute on the classes. These tables are:

1. TBL_City
2. TBL_Country

Data Annotation Attributes are widely used in validating input controls placed on the view. We have covered there uses in the article called Model Validation in ASP.NET Core from Beginning to Expert.

The table called TBL_City has:

KeyId column as primary key.
CityName column with data type varchar(25).
FKid as foreign key column.

Since the Population property has [NotMapped] attribute so no column is made for it on the TBL_City table.

The table called TBL_Country has:

KeyId column as primary key.
Name column with data type nvarchar(20).

See the below image which shows the snapshot of these 2 database tables.

Common Entity Framework Core Data Annotations

Attribute	Description
Table	Applied on entity class to give a name to database table.
Column	Applied on a property to give column name, order and data type.
Key	Sets the property as primary key for the table.
ForeignKey	Applied to a property to mark it as foreign key.
NotMapped	Can be applied to entity class or property for not generating a corresponding table or column in the database.
MaxLength	Sets the max length for the table column.
Required	Can be applied on properties to make the corresponding column on the table as not null.